This application is based on patent application No. 11-44284 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the invention
The present invention relates to a projection image display optical system, e.g., a projection image display optical system suitable for use in projection image display devices such as a head-mounted display (HMD) which projects a two-dimensional image displayed on a liquid crystal display (LCD) onto the pupil of an observer who views an enlarged virtual image.
2. Description of the Related Art
Heretofore, there have been a number of proposed eyepiece optical systems having a so-called pancake structure wherein a flat two-dimensional projection image is enlarged and viewed using a reflection-transmission surface. For examples, U.S. Pat. No. 3,443,858 discloses an eyepiece optical system provided with a flat reflection-transmission surface and a concave transmission surface on the pupil side, and Japanese Laid-Open Patent No. 7-120679 discloses an eyepiece optical system provided with two severely concave reflection-transmission surfaces on the pupil side.
In the assembly of the reflection-transmission surface proposed in the specification of U.S. Pat. No. 3,443,858, however, it is difficult to achieve a wide angle of field due to restrictions of spherical aberration and image surface curvature. One proposed example forms a curved aerial image via a projection relay system to correct image surface curvature, but the construction of the projection relay system is not specifically shown by way of examples and according to the described layout it is difficult to achieve a wide field of view exceeding 60xc2x0. On the other hand, although a wide field of view can be achieved according to the assembly of the reflection-transmission surface disclosed in Japanese Laid-Open Patent No. 7-120679, the device is expensive because a large two-dimensional projection image display element must be used. Furthermore, a wave plate and cholesteric liquid crystal surface are used to form the reflection-transmission surface so as to eliminate direct light using polarization, but forming the two reflection-transmission surfaces is difficult because both are curved surfaces.
An object of the present invention is to provide an improved projection image display optical system.
Another object of the present invention is to provide a projection image display optical system using a compact display element.
Still another object of the present invention is to provide a projection image display optical system having a wide angle of field capable of high resolution projection image display.
These objects are attained by a projection image display optical system provided with a relay optical system, for forming an intermediate image of a two-dimensional projection image, and an eyepiece optical system for projecting an enlarged virtual image of the intermediate image on the pupil of an observer, wherein the image surface of the intermediate image has a convex shape relative to the pupil, and the eyepiece optical system includes sequentially from the pupil side a first reflection-transmission surface, and a second reflection-transmission surface that is concave on the pupil side, and wherein the equation 0.4 less than dR/fs less than 1.8 is satisfied, where dR represents the axial distance between the first reflection-transmission surface and the second reflection-transmission surface, and fs represents the focal length of the eyepiece optical system.